This invention relates generally to a method and apparatus for filtering blood in a blood vessel of a patient.
Blood clot filtering devices have heretofore been provided to filter blood for clots such as emboli and thrombi in a patient's blood vessel. Certain of these devices were designed. to be permanently remotely placed in a blood vessel and included an anchoring means to prevent the migration of the filter from one point to another within the blood vessel. Once the filtering device was remotely placed within the vessel, the device was left indefinitely. An example of such a blood clot filtering device is disclosed in U.S. Pat. No. 4,619,246 issued to Molgaard-Nielsen et al. This reference shows the use of a collapsible filter basket adapted to be introduced into a blood vessel for the purpose of entrapping thrombi and emboli in the blood flowing through the vessel. The Molgaard-Nielsen device is designed to be placed remotely within a blood vessel. A plurality of anchoring legs are secured to a filter basket. The free end of each leg is bent outwardly to form a hook. When the filter basket is positioned in a blood vessel, each hook penetrates slightly into the wall of the vessel so as to hold the filter basket in position.
A device described by Driller et al. in a 1976 technical article is another example of a permanently placed vena cava filter. Such device consists of an open cone formed by straight strands of thin stainless steel wire. Each wire strand has three barbs at the tip to hold the filter basket at one location within the vessel. The strands are joined together at a central hub. In order to place the filter, a plug-ended wire guide is inserted into a length of polyethylene tubing. The collapsed filter is placed in the distal end of a length of polyethylene tubing with the filter hub in the proximal position. The plug-end of the wire guide is then brought into contact with hub of the filter. A Touhy clamp is attached to the proximal end of the tubing. The Touhy clamp permits the plug-ended guide to be securely held a few centimeters proximal the filter while the catheter is advanced. In this way the filter will not be inadvertently ejected. The loaded tubing is then introduced into the jugular vein and advanced under fluoroscopy into the subrenal inferior vena cava. The Touhy clamp is loosened and the plug-end of the wire guide is then advanced to contact the filter. The filter is ejected by withdrawing the tube sleeve while the filter is kept stationary during ejection by the plug-ended wire guide. The strands spring out as the tubing is withdrawn from about the filter. The guide wire and tubing are then withdrawn.
Another device which is designed to filter blood for clots in a blood vessel of a patient is described by Major et al. in a 1974 technical article. This device consists of a multiple ribbed catheter which is introduced through the saphenous vein. After passage into the vena cava, the ribs of tile catheter are extended to contact the cava wall. This produces a sieve through which blood will flow but which will entrap emboli. After the filtering portion is positioned in the vena cava, the tubing which extends proximally from the patient's body is severed and the device is left in place indefinitely until the patient's risk of pulmonary embolism had passed.
The above and other similar prior art devices have the disadvantage that the filter remains in contact with the interior wall of the vena cava for a substantial period of time at the same location with the result that the filter becomes endothelialized and hence attached to tile interior wall of vena cava. This condition tends to block flow of blood in the vena cava and often results in trauma to the interior wall of the vein when tile filter is torn free from its attachment with the wall.